Dosimetric and Biologic Characteristics of the Flattened and the Flattening-Filter-Free Beams of the TrueBeam System.

摘要

In recent years, the potential application of the flattening-filter-free (FFF) photon beam in modern linac systems have been a topic of significant interest. Compared to flattened beams, FFF beams have some apparent advantages, including reduced treatment time, lower scatter to organs at risk (OARs) and decreased neutron contamination. The primary objective of the research in this thesis has been to investigate the dosimetric and biologic characteristics of the flattened beam and the FFF beam of the TrueBeam (TB) system. Using Monte Carlo (MC) simulations, we have also investigated the possibility of further reducing the dose to OARs from the treatments delivered with 6 MV FFF beams. This project includes two different parts. In the first part, we evaluated the differences in treatment plans between the flattened beam and the FFF beam. In the second part, based on the VirtuaLinac system, a MC model was built to simulate the TB system. Based on our findings, we propose the concept of the SPECTER (soft-spectrum-filter) to further reduce the dose to OARs from 6 MV FFF beam using the static IMRT techniques. Clinical cases were used to investigate the impact of the SPECTER on the dose distributions. In the future direction of the project, field size specific design of the SPECTER will be described.